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My unit is approx. 16 years old and on its last leg. The tag on it is worn so badly that you can't get any information on its size or anything else. I can't even tell what make/model it is. My house is approx. 1500 sq. ft. with a tray/vaulted ceiling (no attic) upstairs which makes for more sq. footage to be heated/cooled. What size unit should I replace this one with? Also, what size ducts should I have coming into the house to support the new unit? Any assistance is greatly appreciated.

Originally posted by air of honesty Don't overlook the value of upgrading infiltration sealing, insulation and windows. This can significantly lower the size of the unit required and the bill from now on.

Great advice,too often overlooked.

When it's time to replace,run a Manuel.J ,with and without upgrades to ,insulation windows ,etc..Often the price to upgrade attic insulation is very low,and can reduce the size system needed by 1/2 ton.

So if it's a 3 ton and goes down to 2.5 ton,you save 16% operating cost,without changing the SEER of the system ,old versus new.Though you'll likely want a higher SEER,for even more savings.

Reducing the tonnage can help a lot,IF your ducts are undersized for the current system!

These upgrades without ,decreasing the size of the system,can leave you with an oversized system,and humidity control problems in the cooling season.